feat: add binding for external data

[maximepvrt]

External variables binding for #2053

I've implemented a feature that allows for external variable binding within the Nuxt Content. This enhancement enables seamless integration of external variables into the project, thereby enhancing its functionality and flexibility.

I remain enthusiastic about contributing to the Nuxt Content project and ensuring its continued growth and improvement.

<template>
  <div>
    <ContentRendererMarkdown :value="data" :data="mdcVars"/>
    <button type="button" v-on:click="mdcVars.name = 'Hugo'">Change name</button>
  </div>
</template>

<script setup lang="ts">
const { data } = await useAsyncData(() => queryContent('test').findOne());
const mdcVars = ref({ name: 'Maxime'});
</script>

test.md

# Hello {{ $doc.name }}

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[maximepvrt]

local pnpm test is ok

Test Files 10 passed (10)
Tests 394 passed (394)
Start at 17:14:29
Duration 43.15s (transform 592ms, setup 0ms, collect 3.21s, tests 227.62s, environment 1ms, prepare 924ms)

[maximepvrt]

🙏 @farnabaz

[farnabaz]

Thanks ❤️